Roller bearings of the type called cross-roller bearing because the rollers are arranged in circular direction in a fashion any the adjacent rollers are alternately tilt in opposite direction to each other in recent years have been increasingly incorporated in swiveling and/or rocking components of a variety of machinery including industrial robots, machine tools, medical appliances, optical instruments, and so on. Thus, various cross-roller bearings different in style, construction and size have been developed commercially in conformity with their usage and have done more to make the machines and instruments miniature as well as lightweight.
Of some commonly-assigned Japanese patent applications concerned with rolling-contact bearings, the commonly-assigned Japanese Laid-Open Patent Application 2005-180 578 discloses a cross-roller bearing with plug and production thereof in which inner and outer rings each are made in an one-piece construction and combined with each other to define a race between them, the outer ring having an opening to introduce rollers into the race, and a plug to fit into the opening after introduction of the rollers into race, thereby sealing up the opening. The cross-roller bearing constructed as stated just earlier has rigidity or stiffness enough to bear against revolutions at high speed following up high-speed turning of the machines without getting jarred. The cross-roller bearing is also easier to manufacture with accuracy. Moreover, the outer ring has an oil hole to feed the raceway with lubricant.
Disclosed for example in Japanese Laid-Open Patent Application 2001-99 144 is another example of the thin rolling-contact bearing, which is suited for use in the articulations of robot arms. The prior bearing is envisaged getting easily downsized, easier and cost-saving in machining of parts or members of the articulations to fit the bearing into there. With the prior thin rolling-contact bearing recited just above, the inner and outer rings are set to have the largest radial widths, respectively, which are each 1.5 times or more as large as the maximum axial thickness of them to make it possible to ensure high rigidity in the bearing irrespective of reduction in axial thickness. The large radial widths of the inner and outer rings can afford to provide ample spaces around the circular inside edge of the inner ring and the circular outside edge of the outer ring to have some holes that are used to fasten the bearing to any other member or component, getting unnecessary any conventional housing to support a shaft fitted into the inner ring while accommodate the outer ring, thereby contributing to compactness and cost-saving of the bearing. Moreover, there is no retainer or separator to space balls that fit for rolling movement into the annular raceway defined between the inner and outer rings.
With the prior cross-roller bearing with plug recited above, nevertheless, there is a practical issue in downsizing or reduction as the inner and outer rings both made thicker in size. Next, the thin rolling-contact bearing constructed as stated earlier, although most convenient for simple usage as the rolling elements are balls, is unfit for revolution with high turning accuracy and also insufficient for smooth turning performance with permitting different loads or composite loads.
Modern advanced machines including industrial robots, optical instruments, medical appliances, and so on are increasingly needed to be nimble in their operations even with more downsized than ever. For instance, the bearing to support a robot arm for swiveling movement around the pivot is required having such rigidity or stiffness that permits any load weighed at the top of the arm, or every load different in the direction of moment. Moreover, the parts or members to be incorporated into the swiveling and/or rocking components are desired to be most compact or most lightweight to keep the inertia weight of the arm less. To cope with this, selection of the cross-roller bearing is preferred.
The modern articulations of the robot arms which desires the bearing having the inner ring of 50 mm or less in inside diameter, however, hope to find the cross-roller bearing more compact and lightweight than ever into the ultrathin construction.